1. Field of the Invention
This invention relates in general to an apparatus and method for a power device assembly, and more particularly, to an apparatus and method for integrating power device assembly into a SMD (Surface Mounted) assembly line.
2. Description of Related Art
High power devices in a chip, such as transistors, have high heat dissipation. To cool down the high power devices effectively, a low thermal resistance from the device to the outside is required. To make a low thermal resistance, manufacturers often use a metallic flange at the bottom of a high power device. The metallic flange attaches the power device to a mechanical member, such as a heat sink. The heat in the power device can be easily dissipated to the heat sink through the metallic flange.
In a chip assembly line, to address the heat dissipation problem, a power device with a flange is usually attached to a printed circuit board through a hole in the printed circuit board with two screws. The power device connects to the printed circuit board at its electric leads coming to the device and going out of the device. The metallic flange itself is to be attached to the mechanical member under the printed circuit board. FIGS. 1 and 2 illustrate a traditional attaching method between the metallic flange and the mechanical member. In FIGS. 1 and 2, a printed circuit board 100 has a hole 102 to receive an active high power device 104. The device 104 has two electric leads 106,108. The two leads 106,108 are soldered to conductive strips 110,112, respectively on the printed circuit board. The device 104 includes a device portion 114 and a flange portion 116. The flange portion 116 is attached to the bottom of the device portion 114. Screws 118, 120 are used to mount the flange portion 116 of the device 104 onto a mechanical member 122. In FIG. 2, a cover 124 is used to enclose the assembled printed circuit board 100 between the cover and the mechanical member 122. The heat generated in the device 104 is dissipated to the mechanical member 122 via the flange portion 116 of the device 104. To ensure a low thermal resistance between the device 104 and the mechanical member 122, the screws 118,120 are used to fixedly attach the flange portion 106 to the mechanical member 122.
Accordingly, a traditional method of assembling electrical components including the above active high power device on the printed circuit board requires at least the following phases in the assembly line:
1. SMD (Surface Mounted) components are assembled by a pick and place machine and mounted on the printed circuit board; PA1 2. SMD components are soldered in a reflow oven; PA1 3. The printed circuit board is attached to the mechanical member with a few screws (other than the screws 118,120) to fix the printed circuit board in place; PA1 4. The active power device with the flange portion is placed in the hole of the printed circuit board; PA1 5. The screws (118,120) are assembled and tightened to fix the flange portion of the device to the mechanical member; PA1 6. The electric leads of the device are soldered by hand; and PA1 7. The cover is attached onto the top of the printed circuit board by a few screws (other than the screws 118,120). PA1 Additional phases (e.g. the above phases 3-6) are required in comparison to the phases used in a normal SMD (Surface Mounted) reflow process. Thus, the assembly makes the manufacturing process slow and expensive. PA1 Hand soldering is required. The amount of soldering materials, e.g. tin, has an effect on an RF performance of the device. This effect would cause a process variation and a degraded yield.
The traditional method has at least the following disadvantages:
Accordingly, it can be seen that there is a need for an apparatus and method for integrating the power device assembly into a SMD (Surface Mounted) assembly line. There is also a need for such an apparatus and method still resolving the heat problem in an active high power device.